- nvmem: Add driver to expose reserved memory as nvmem (jsc#SLE-SLE-16616).
    - Update config files: Enable nvmem-rmem as module on arm64 & armv7+lpae, disable it otherwise
    
    This is needed early to get boot-loader configuration working on RPi4;
    an essential feature.
    
    Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>